Yep, my buns do the same thing. Maybe it is because it’s more dry, or maybe some batches have a different and bad taste which is not something we can see. If you just recently received the box, you can try contacting SPS and telling them your bun won’t eat it. They might offer to replace it with a new box of the same quantity.

You could also donate the box of hay to a local rabbit rescue or a shelter that takes in rabbits, instead of throwing it out. 

Buns eat the freshest pieces of hay first, then go for the “left overs.” If you’re sure there isn’t mold (in between the layers or at the bottom of the box?), then it’s possible that the hay from the old box just happens to be fresher than the hay from the new box. Even if two piles of hay look and smell the same to us, buns can differentiate between which one is “the best” pile.

As Rio and Buns suggested, you can try contacting SPS and ask for a replacement order, and donating the hay to a rabbit rescue is an awesome idea .